Metallic nickel-based acid-resistant material

ABSTRACT

A nickel-molybdenum-iron alloy with high corrosion resistance with respect to reducing media at high temperatures, consisting of (in % by mass): 61 to 63% nickel, 24 to 26% molybdenum, 10 to 14% iron, 0.20 to 0.40% niobium, 0.1 to 0.3% aluminum, 0.01 to 1.0% chromium, 0.1 to 1.0% manganese, at most 0.5% copper, at most 0.01% carbon, at most 0.1% silicon, at most 0.02% phosphorus, at most 0.01% sulphur, at most 1.0% cobalt, and further smelting-related impurities.

The invention relates to a metallic material with resistance in moderately concentrated sulfuric acid and hydrochloric acid solutions at high temperatures.

Sulfuric acid is one of the most important basic substances of the chemical industry. Sulfuric acid has a broad spectrum of application in the chemical industry, wherein it is used at different temperatures and in different concentrations. This imposes a different corrosive stress on the metallic materials used for its handling. As a rule this increases with the temperature, until ultimately corrosion resistance no longer exists. The respective upper application limit is plotted in so-called isocorrosion diagrams in dependence on the concentration of the sulfuric acid.

FIG. 1 shows an example of such an isocorrosion diagram, containing the comparative plot of the resistance of various known metallic materials in pure sulfuric acid (Metals Handbook, 9th Edition, Vol. 13: Corrosion, ASM International, Metals Park, Ohio 44073, 1987). Therein the 0.5 mm/year isocorrosion lines are shown as a measure of the resistance of different known metallic materials. Below these lines, the resistance ranges of the respective associated materials are located by definition in the present case. In FIG. 1, it is evident that the resistance range of the stainless steel labeled Type 316 becomes significantly smaller with increasing concentration at first, then as the concentration increases further ultimately becomes larger again at higher temperatures. According to this diagram, the nickel alloys such as C-276, 625, G-3/G-30, Alloy 20 and finally the nickel-molybdenum alloys B/B-2 lie above this, and therefore have much better resistance.

An isocorrosion diagram such as shown in FIG. 1 is valid for the experimental or operating conditions under which it was ascertained. On the one hand, different limit values, for example 0.1 mm/year isocorrosion lines, can be agreed instead of the 0.5 mm/year isocorrosion lines. On the other hand, the nature and concentration of the admixtures present in the sulfuric acid during industrial practice can have significant influence on the corrosion resistance. Nevertheless, it is clear from FIG. 1 that, in the temperature range up to 130° C. to be considered, obviously only the nickel-molybdenum alloys B/B-2 have, according to the previous state of the art, sufficient corrosion resistance within a broader interval of the sulfuric acid concentration. The disadvantages of these nickel-molybdenum alloys B/B-2 according to the previous state of the art lie primarily in the high raw material costs and thus high metal values for their alloying elements, consisting very extensively of nickel and molybdenum.

Thus the alloy B-2, which is N10665 according to UNS (Unified Numbering System) or 2.4617 according to EN (European Standard), and which is now very common here, consists of (values in % by mass) 26 to 30% molybdenum, max. 2% iron, max. 1% chromium, max. 1% manganese, max. 0.08% Si and max. 0.01% carbon, the remainder being essentially nickel. This typically means a nickel proportion of, for example, 69% by mass (see High-Alloy Materials, Corrosion Behavior and Use, TAW Verlag, Wuppertal 2002, p. 192).

In the more recent past, attempts have been made, with alloys such as B-3 (UNS N10675), for example, to raise the alloying contents of the less expensive alloying elements iron, chromium and manganese to (values in % by mass) 1 to 3% iron, 1 to 3% chromium and max. 3% manganese, wherein a nickel content of 68% by mass is cited as an example (see High-Alloy Materials, Corrosion Behavior and Use, TAW Verlag, Wuppertal 2002, p. 192). For the previously common predecessor alloy B, an iron content of 4 to 6% by mass is given in accordance with UNS N10001.

From U.S. Pat. No. 3,649,255, a corrosion-resistant nickel-molybdenum alloy was disclosed with (in % by mass) 20 to 40% Mo, up to 10% Fe, up to 4% Co, up to 5% Cr, up to 2% Mn, up to 0.03% P, up to 0.03% S, up to 0.1% C, up to 0.1% Si, 0.1 to 1.0% V, 0.001 to 0.035% B, 0.01 to 1% Zr, remainder Ni and unavoidable impurities. Average contents of Mo should be 26 to 32% and of Fe up to 7%. As an example, Co is given as 1.01%.

DE 42 10 997 relates to an austenitic nickel-molybdenum alloy of the following concentration (in % by mass): Mo 26-30%; Fe 1-7%, Cr 0.4-1.5%, Mn up to 1.5%, Si up to 0.05%, Co up to 2.5%, P up to 0.04%, S up to 0.01%, Al 0.1-0.5%, Mg up to 0.1%, Cu up to 1.0%, C up to 0.01%, N up to 0.01%, remainder Fe.

The task of the present invention is to find a metallic material that is resistant in 20 to 80% sulfuric acid at high temperatures up to 130° C., that at the same time has sufficient resistance on the cooling water side and that above all has a much lower metal value in comparison with the common metal alloys according to the state of the art.

This task is accomplished by a nickel-molybdenum-iron alloy with high resistance relative to reducing media at high temperatures, consisting of (in % by mass)

Ni 61-63% Mo 24-26% Fe 10-14% Nb 0.20-0.40%   Al 0.1-0.3%  Cr 0.01-1.0%   Mn 0.1-1.0%  Cu max. 0.5% C max. 0.01% Si max. 0.1% P max. 0.02% S max. 0.01% Co max. 1.0% and further impurities from smelting.

Advantageous further developments of the inventive alloy are to be inferred from the associated dependent claims.

One advantageous alloy consists of (in % by mass)

Ni 61.5-62.5%  Mo 24.5-26.0%  Fe 10.5-13.5%  Nb 0.2-0.4% Al 0.1-0.3% Cr 0.01-1.0%  Mn 0.1-0.8% Cu max. 0.5% C max. 0.01% Si max. 0.1% P max. 0.02% S max. 0.01% Co max. 1.0%.

A further preferred alloy consists of (in % by mass)

Ni 61.5-62.5%  Mo 24.8-26.0%  Fe 10.5-12.5%  Nb 0.2-0.4% Al 0.1-0.3% Cr 0.01-0.9%  Mn 0.1-0.5% Cu max. 0.3% C max. 0.008% Si max. 0.08% P max. 0.015% S max. 0.008% Co max. 1.0%.

According to a further concept of the invention, the inventive alloy is usable for components with high corrosion resistance toward reducing media, especially hot moderately concentrated sulfuric acid and hydrochloric acid solutions.

The preferred area of application of the inventive alloy is seen in the field of chemical systems, since here larger cases of use are seen for reducing media at higher temperatures.

The use of the alloy as a rod-like weld filler of like material and/or for welding of nickel-molybdenum alloys is also conceivable.

The inventive alloy can be used, for example, as a wrought material for the production of sheets, strips, wires, bars, forgings and tubes and as castings.

Surprisingly, it has been found that the disadvantageous situation of the state of the art characterized by the high metal values of nickel and molybdenum can be appreciably alleviated if a nickel-molybdenum-iron alloy specified in advance is employed for the handling of hot sulfuric acid. The average content of nickel is advantageously between 61 and 63% by mass. This means a reduction of 6 to 7% by mass of the expensive alloying element nickel compared with the state of the art outlined initially as an example. The content of the alloying element molybdenum, which likewise is expensive, lies between 24 and 26% by mass on average, which is also clearly below that of the state of the art cited for the nickel-molybdenum alloys with 27 to 28% by mass for example (see High-Alloy Materials, Corrosion Behavior and Use, TAW Verlag, Wuppertal 2002, p. 192).

This is illustrated in detail in the following.

TABLE 1 Chemical composition of the investigated nickel- molybdenum-iron alloys according to determination by spectral analysis in comparison with a nickel-molybdenum alloy B-2 according to the state of the art in the literature (see High- Alloy Materials, Corrosion Behavior and Use, TAW Verlag, Wuppertal 2002, p. 192). Alloying element, % by mass Alloy Ni Mo Fe Cr Nb V Mn Cu Al According to 50 62.2 25.6 11.2 0.02 0.33 0.01 0.28 0.01 0.25 the invention 44 61.8 25.4 11.8 0.02 0.34 0.01 0.29 0.01 0.27 Outside the 51 63.3 20.4 11.6 0.63 0.01 2.34 0.30 1.00 0.26 invention 45 60.1 21.8 14.7 2.10 0.56 0.01 0.19 0.17 0.28 State of the art B-2 69 28 1.7 0.7 not given

Table 1 shows inventive nickel-molybdenum-iron alloys in comparison with nickel-molybdenum-iron alloys falling outside the invention and with the nickel-molybdenum alloy B-2 associated with the state of the art. Some admixtures and impurities from smelting are not listed. It is evident that iron contents between 11 and 12% by mass were tested, as was an iron content of 14.7% by mass in one case, in comparison with the iron content of only 1.7% by mass, which is given as an example for the alloy B-2 according to the state of the art. The tested molybdenum contents lie between 20.4 and 25.6% by mass, in comparison with the molybdenum content of 28% by mass, which is given as an example for the alloy B-2 according to the state of the art. The tested nickel contents lie between 60.1 and 63.3% by mass, in comparison with the nickel content of 69% by mass, which is given as an example for the alloy B-2 according to the state of the art.

Table 2 shows the corrosion losses of the alloys listed in Table 1.

TABLE 2 Corrosion loss of the inventive embodiments 50 and 44 of the investigated nickel—molybdenum—iron alloy in hot moderately concentrated sulfuric acid in comparison with two nickel—molybdenum—iron alloys 51 and 45 falling outside the invention as well as in comparison with that of a nickel—molybdenum alloy B-2 according to the state of the art. Corrosion loss in g/m²h over 24 h 30% H₂SO₄ at 50% H₂SO₄, 80% H₂SO₄ at Alloy 100° C. boiling 130° C. According to 50 0.11 0.13 0.71 the invention 44 0.16 not determined 0.16 Outside the 51 0.20 0.99 4.70 invention 45 0.25 not determined 1.13 State of the B-2 0.10 0.12 0.08 art

Table 2 shows the corrosion loss of the inventive embodiments 50 and 44 of the investigated nickel-molybdenum-iron alloy in hot moderately concentrated sulfuric acid in comparison with two nickel-molybdenum-iron alloys 51 and 45 falling outside the invention as well as in comparison with the nickel-molybdenum alloy B-2 according to the state of the art. The corrosion loss of the inventive embodiments 50 and 44 is below the 0.5 mm/year isocorrosion line of FIG. 1, except for that of the inventive embodiment 50 in 80% H₂SO₄ at 130° C.

The corrosion resistance of the welded joints of the inventive embodiment 50 of the investigated nickel-molybdenum-iron alloys in hot moderately concentrated sulfuric acid (30 and 50%) is similar to that of the unwelded condition.

The inventive embodiment 50 of the investigated nickel-molybdenum-iron alloys exhibited a corrosion loss of 0.08 mm/year in the immersion test in 4% salt solution at 150° C. over 120 hours. This means an adequate resistance, in conformity with the set task, on the cooling-water side even in cooling waters highly contaminated with chloride.

The mechanical characteristics of the inventive embodiment 44 of the investigated nickel-molybdenum-iron alloys determined in the tension test at room temperature were Rp_(0.2)≧350 N/mm², Rp_(1.0)≧380 N/mm², Rm≧760 N/mm² and A₅≧40%, which are comparable with those of the nickel-molybdenum alloy B-2 according to the state of the art (see Sheet and Plate—High Performance Materials; Publication No. N 554 98-10 of Krupp VDM GmbH, pp. 34/35), whereas the embodiment 45 of the investigated nickel-molybdenum-iron alloys falling outside the invention did not achieve the cited strength values. 

1: Nickel-molybdenum-iron alloy with high resistance relative to reducing media at high temperatures, consisting of (in % by mass) 61 to 63% nickel 24 to 26% molybdenum 10 to 14% iron 0.20 to 0.40% niobium 0.1 to 0.3% aluminum 0.01 to 1.0% chromium 0.1 to 1.0% manganese max. 0.5% copper max. 0.01% carbon max. 0.1% silicon max. 0.02% phosphorus max. 0.01% sulfur max. 1.0% cobalt and further impurities from smelting.
 2. Alloy according to claim 1, with (in % by mass) 61.5 to 62.5% nickel 24.5 to 26.0% molybdenum 10.5 to 13.5% iron 0.2 to 0.4% niobium 0.1 to 0.3% aluminum 0.01 to 1.0% chromium 0.1 to 0.8% manganese max. 0.5% copper max. 0.01% carbon max. 0.1% silicon max. 0.02% phosphorus max. 0.01% sulfur max. 1.0% cobalt.
 3. Alloy according to claim 1, with (in % by mass) 61.5 to 62.5% nickel 24.8 to 26.0% molybdenum 10.5 to 12.5% iron 0.2 to 0.4% niobium 0.1 to 0.3% aluminum 0.01 to 0.9% chromium 0.1 to 0.5% manganese max. 0.3% copper max. 0.008% carbon max. 0.08% silicon max. 0.015% phosphorus max. 0.008% sulfur max. 0.02% nitrogen max. 0.012% magnesium max. 1.0% cobalt.
 4. Use of the alloy according to claim 1 for components with high corrosion resistance toward reducing media, especially hot moderately concentrated sulfuric acid and hydrochloric acid solutions.
 5. Use of the alloy according to claim 1 for components in chemical plants.
 6. Use of the alloy according to claim 1 as a weld filler of like material and for welding of nickel-molybdenum alloys.
 7. Use of the alloy according to claim 1 as a wrought material for the production of sheets, strips, wires, bars, forgings and tubes and as castings. 